This invention relates generally to writing or marking instruments, and particularly to those of the kind having a writing tip retractable into the body of the instrument when it is not in use. More particularly, the invention deals with improvements in a clip-operated retraction mechanism for such writing instruments.
Japanese Unexamined Utility Model Nos. 61-107590 and 62-5986 are hereby cited as teaching retractable-tip writing instruments of simplified construction to which the present invention bears particular pertinence. Basically, these prior art devices are akin in having a pocket clip formed in one piece with a push button via a fulcrum or flexible joint. The clip fulcrum takes the form of a short pin, with a constriction formed at its midpoint, extending through a clearance slot in the substantially tubular body of the instrument. The push button is affixed to one end of an ink reservoir which has a writing tip at the other end and which is mounted within the body for movement in its longitudinal direction. The reservoir is sprung with respect to the body in a direction away from the tip.
Constituting the retraction mechanism of this prior art device is the pocket clip which has a catch formed thereon. The catch plunges into a recess in the body when the push button is pressed against the bias of the spring. The reservoir is then locked in the writing position with respect to the body.
This known type or retraction mechanism has had some inherent weaknesses in connection with the fulcrum integrally joining the clip to the push button. The fulcrum has had to coact with the clip to urge the catch against the body, in order that the catch may infallibly fall into the recess in the body when the push button is pressed. Additionally, the fulcrum has had to permit the clip to be manually pivoted thereon for the movement of the catch into and out of the recess.
Thus the fulcrum has had to perform two contradictory functions. One is as a resilient joint urging the catch against the body. The other is as a pivot about which the clip is turned for the movement of the catch into and out of the recess in the body. The fulcrum has therefore been susceptible to breakage, particularly at its constricted midsection, as a result of repeated application of stresses in use of the writing instrument. The fulcrum has been all the more prone to breakage as it has had to serve the additional purpose of preventing the angular displacement of the push button when it is pressed, by sliding along the edges of the body bounding the slot therein.